When looking at whether Azure premium storage is necessary, IOPS (input/output operations per second) is a good metric/guideline to look at. Does Sitecore provide any recommendations/guidelines as to what range is recommended for content management, content delivery and SQL Servers? Sitecore does provide guidance for Mongo servers, as they are known for needing specific IOP levels. I am looking for specific numbers for the other server roles.
I am not aware any IOPS guidelines, but there is a Sitecore Experience Platform 8.2 Performance White Paper where they have made many test and the Premium Storage Account is only mentioned for MongoDB.
In general, your Primary MongoDB takes the biggest hit and needs the fastest drives. Other than that, Sitecore solutions have largely been found to be CPU bound, rather than bound by performance of drives and storage systems.